MyBatis自动配置原理

MyBatis自动配置原理

在springboot中，mybatis引用的jar包

 
     org.mybatis.spring.boot
     mybatis-spring-boot-starter
     2.1.3

mybatis的配置一般放在application.yml文件中

mybatis:
  mapper-locations: classpath:mybatis/mapper/*Mapper.xml
  type-aliases-package: com.xxx.xlt.model.po

mybatis自动配置主要跟mybatis-spring-boot-autoconfigure有关，该jar包中的MybatisProperties可以读取application.properties文件中以mybatis开头的配置信息

@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {

  public static final String MYBATIS_PREFIX = "mybatis";

  private static final ResourcePatternResolver resourceResolver = new PathMatchingResourcePatternResolver();

  
  private String configLocation;

  
  private String[] mapperLocations;

  
  private String typeAliasesPackage;

  
  private Class typeAliasesSuperType;

  
  private String typeHandlersPackage;

  
  private boolean checkConfigLocation = false;

  
  private ExecutorType executorType;

  
  private Class defaultscriptingLanguageDriver;

  
  private Properties configurationProperties;

  
  @NestedConfigurationProperty
  private Configuration configuration;
}

在应用启动过程中就会读取配置文件中的mybatis配置信息

MybatisAutoConfiguration可以实现mybatis的自动配置，他的说明原文是这样的

Auto-Configuration for Mybatis. Contributes a SqlSessionFactory and a SqlSessionTemplate. If org.mybatis.spring.annotation.MapperScan is used, or a configuration file is specified as a property, those will be considered, otherwise this auto-configuration will attempt to register mappers based on the interface definitions in or under the root auto-configuration package.

意思是说：自动配置mybatis, 生成一个SqlSessionFactory和SqlSessionTemplate的bean。如果使用了@MapperScan注解或者是一个配置文件被指定为一个属性，这些将会被考虑。否则，自动配置将会尝试基于在自动配置根package下的接口定义去注册mappers.

@org.springframework.context.annotation.Configuration
// SqlSessionFactory和SqlSessionFactoryBean位于类路径上时实例化bean   
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
// 自动装配一般使用，beanFactory包含了指定的bean的时候，条件匹配
@ConditionalOnSingleCandidate(DataSource.class)
// 开启MybatisProperties.class的自动参数映射
@EnableConfigurationProperties(MybatisProperties.class)
// 在DataSourceAutoConfiguration,MybatisLanguageDriverAutoConfiguration初始化之后，进行自动配置
@AutoConfigureAfter({ DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class })
public class MybatisAutoConfiguration implements InitializingBean {
  private final MybatisProperties properties;

  private final Interceptor[] interceptors;

  private final TypeHandler[] typeHandlers;

  private final LanguageDriver[] languageDrivers;

  private final ResourceLoader resourceLoader;

  private final DatabaseIdProvider databaseIdProvider;

  private final List configurationCustomizers;
	// bean初始化时执行
  @Override
  public void afterPropertiesSet() {
    checkConfigFileExists();
  }

  private void checkConfigFileExists() {
    if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) {
      Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation());
      Assert.state(resource.exists(),
          "Cannot find config location: " + resource + " (please add config file or check your Mybatis configuration)");
    }
  }
    
    // beanFactory中缺少SqlSessionFactory时会初始化一个
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    factory.setDataSource(dataSource);
    factory.setVfs(SpringBootVFS.class);
    if (StringUtils.hasText(this.properties.getConfigLocation())) {
 factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
    }
    applyConfiguration(factory);
    if (this.properties.getConfigurationProperties() != null) {
      factory.setConfigurationProperties(this.properties.getConfigurationProperties());
    }
    if (!ObjectUtils.isEmpty(this.interceptors)) {
      factory.setPlugins(this.interceptors);
    }
    if (this.databaseIdProvider != null) {
      factory.setDatabaseIdProvider(this.databaseIdProvider);
    }
    if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
      factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
    }
    if (this.properties.getTypeAliasesSuperType() != null) {
      factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
    }
    if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
      factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
    }
    if (!ObjectUtils.isEmpty(this.typeHandlers)) {
      factory.setTypeHandlers(this.typeHandlers);
    }
    if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
      factory.setMapperLocations(this.properties.resolveMapperLocations());
    }
    Set factoryPropertyNames = Stream
        .of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
        .collect(Collectors.toSet());
    Class defaultLanguageDriver = this.properties.getDefaultscriptingLanguageDriver();
    if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
      // Need to mybatis-spring 2.0.2+
      factory.setscriptingLanguageDrivers(this.languageDrivers);
      if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
        defaultLanguageDriver = this.languageDrivers[0].getClass();
      }
    }
    if (factoryPropertyNames.contains("defaultscriptingLanguageDriver")) {
      // Need to mybatis-spring 2.0.2+
      factory.setDefaultscriptingLanguageDriver(defaultLanguageDriver);
    }

    return factory.getObject();
  }
    
    // beanFactory中缺少SqlSessionTemplate时会初始化一个 
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
    ExecutorType executorType = this.properties.getExecutorType();
    if (executorType != null) {
      return new SqlSessionTemplate(sqlSessionFactory, executorType);
    } else {
      return new SqlSessionTemplate(sqlSessionFactory);
    }
  }
}